Powder metal axial and radial retention features for molding applications

ABSTRACT

A powder metal insert for overmolding and method of making it has retention features on the outer surface extending from each end and angularly offset from one another.

CROSS-REFERENCE TO RELATED APPLICATION

This claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/407,294 filed Oct. 27, 2010, which is hereby incorporated by reference for all purposes.

FIELD OF THE INVENTION

This invention relates to sintered powder metal manufacturing and in particular to forming axial and radial locking features in components that will become part of a molded assembly.

BACKGROUND OF THE INVENTION

The use of sintered powder metal (PM) parts has increased in the recent past as a base component or insert that becomes part of a molded product of multi-materials. These materials may be plastic, rubber, aluminum, or another material as required. The advantage of the multi-material product is lower cost, increased productivity and greater design flexibility. These advantages are achieved in part because PM parts can provide added strength and features for the molded component not achievable as a single material product, and PM parts can be manufactured to net-shape or near net-shape in various alloys which yields little material waste and eliminates or minimizes machining.

Typically the PM part will have an inner surface that defines features required for consumer use of the product. This may be a straight through hole, keyway, double D hole, or others as required. The outer surface engages the other component material. This quite often is achieved by molding the material around the PM part often referred to as overmolding. Simple PM parts or inserts might not include any retention features. As such the PM insert may break free and fall out of the component. To address this problem, some inserts may include retaining features to provide a more secure connection to the component. For example, some PM inserts will have a flange to provide retention in one direction, another may have outer surface features such as ribs, a keyway, a polygonal shape and so forth to provide rotary or radial retention. Other designs include knurling, undercuts, or perforations into which the molded material can flow to provide axial retention.

However, to achieve both rotary and axial retention, typically additional processing will be required that significantly increases the overall manufacturing time and cost of the multi-material component. For example knurling, turning, undercutting or milling an undercut or side perforations all require an additional processing step. Considering these limitations of previous designs, a need exists for an improved PM part that has both rotary and axial retention features that is easily manufactured.

SUMMARY OF THE INVENTION

In one aspect the present invention provides a PM part that comprises a first or upper end surface and a second or lower end surface. The distance between the end surfaces defines an axial or longitudinal direction. The PM part further comprises an inner surface that defines a passageway configured as required by consumer use of the product and an outer surface configured to engage a material structure in which the PM part is placed. The distance between the inner and outer surfaces defines a radial direction perpendicular to the axial or longitudinal direction. The PM part further comprises a first set of retention features that project inwardly from the outer surface and longitudinally from the first end surface. A second set of retention features project inwardly from the outer surface and longitudinally from the second end surface. This second set of retention features is angularly located midway between the first set of retention features so that they are angularly offset from one another do not intersect. Both the first and second sets of retention features have at least a portion of the surface that is perpendicular to the tangential direction. Furthermore these features also have a portion of the feature surface that is perpendicular to the longitudinal direction. Thus they provide retention in both the axial or longitudinal direction to resist punch out of the PM part in the axial direction as well as retention in a radial direction so as to resist rotation of the PM part relative to the material surrounding it.

In another aspect the present invention provides a method for forming the part from powder metal. This method includes the step of pressing the powder metal in a longitudinal direction. This can be accomplished utilizing a compaction die set including a lower punch, a lower core, a lower die, an upper die, an upper punch, and an upper core. The top surface of the PM part will be formed by the upper punch. The upper outer surface including the upper retention features will be formed by the upper die cavity. The lower outer surface of the part including the lower retention features will be shaped by the lower die cavity. The lower end face of the part will be formed by the lower punch. The inner surface of the part is shaped with the core. This method further includes removal of the part by first raising the upper die and upper punch from the part and final removal by lowering the lower die and core.

Other features and advantages of the invention will appear in the detailed description which follows. In the description, reference is made to the accompanying drawings which illustrate a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a perspective view of a prior art, powder metal part having knurling and circular undercut features for axial and radial retention;

FIG. 1 b is a sectional view of the same powder metal part of FIG. 1 a showing the part 51 overmolded with another material 52 as a multi-material product;

FIG. 2 a is a perspective view of a powder metal part redesigned to incorporate the present invention;

FIG. 2 b is a sectional view of the same powder metal part of FIG. 2 a showing the part 53 overmolded with another material 54 as a multi-material product;

FIGS. 3 a-3 f are sectional schematic views of the tooling for forming the powder metal part of FIG. 2 a; and

FIG. 4 is a schematic view summarizing which parts of the powder metal part are formed by which parts of the tooling.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In accordance with the present invention, the axial or longitudinal and radial retention features are created during the pressing cycle. As shown in FIG. 2 a, the PM part further comprises an inner surface 90 that defines a passageway configured as required by consumer use of the product, and an outer surface configured to engage a material structure in which the PM part is placed. The distance between the inner and outer surfaces defines a radial direction perpendicular to the axial or longitudinal direction. The PM part further comprises a first set of upper retention features 91 that project inwardly from the outer surface and longitudinally from the upper surface 92. A second set or lower retention features 93 project inwardly from the outer surface and longitudinally from the lower surface 94. This second or lower set if retention features 93 are offset angularly so that they are located on the periphery of the part between the upper retention features 91 so that they do not intersect, were they to be extended into the zone of the other set of retention features. Both sets of retention features extend generally parallel to the axial direction of the part and for less in axial length than the length of the part, so that each feature defines a blind end surface 95, which extends radially and circumferentially and is in a plane that is perpendicular to the axial direction.

As illustrated, both the upper and lower retention features have at least a portion of the surface that is perpendicular to the radial direction and also have a portion of the feature surface that is perpendicular to the longitudinal direction. Thus they provide retention in both the axial direction and in the radial direction.

The process is illustrated in FIGS. 3 a-3 f being performed to make the retention features. As shown in FIGS. 3 a-3 f, a PM insert for overmolding can be made according to the invention using a compaction tooling set that includes as tooling members a lower die 501, an upper die 502, an upper punch 601, an upper pin 701, a lower punch 201, and a lower core pin 101. The tooling members are moved by mechanical, hydraulic or other means of power when installed in a powder metal compacting press.

The starting position is shown in FIG. 3 a. In this position, the die 501 is aligned with the lower tooling members 101 and 201 and the lower tooling members all have their upper surfaces level with one another. The lower punch 201 is tubular and can be retracted relative to the die 501 and core pin 101 so as to surround the core pin 101 below the cavity into which powder metal is filled.

The second step, shown in FIG. 3 b, is moving the tooling members lower core 101 and die 501 relative to lower punch 201 to form a cavity 582. This may occur by moving the punch 201 down or moving the core 101 and die 501 up.

Next in FIG. 3 c the third step is to fill the resulting cavity 582 with powder metal.

The fourth step, FIG. 3 d, is to bring the tooling members upper die 502, upper pin 701 and upper punch 601 down to the position where the upper die 502 is against lower die 501, and upper pin 701 is against lower core pin 101.

The fifth step, FIG. 3 e, is to continue down with the upper die 502, forcing the lower tooling member die 501 to move downward with the powder being held in a relative position by the lower punch 201. The powder cavity 583 is now formed partially by the upper die 502 and partially by the lower die 501.

The sixth step, FIG. 3 f is to continue moving the punches toward each other until the powder is compacted between them. PM compact 585 is formed with the inside shape formed by the core 101 and on the outside shape formed partially by upper die 502 and partially by lower die 501, with the upper die forming retention features from the top surface and the lower die forming retention features from the bottom surface and the upper die 502 and lower die 501 offset angularly in position with the top to bottom retention features angularly offset so that the features of each set are between the features of the other set, with each set providing both axial and radial retention. The alignment of upper die 502 to lower die 501 can be completed with a setting guide tool or additional tooling features can be utilized to facilitate this alignment.

The final or seventh step, FIG. 3 g, is for the upper die 502 to move upward followed by the upper punch 601, then the lower die 501, and lower core 101 moved downward to fully eject the part and return to the starting position.

Thereby, referring to FIG. 4, the inside surface 90 is formed by the core 101, the upper surface 92 is formed by the punch 601, the lower surface 94 is formed by punch 201, the upper outer section 96 is formed by die 502 and the lower outer section 98 is formed by die 501.

Following compaction the part is sintered in a sintering oven to fuse the powder of the compact and solidify it, making it structurally sound while largely maintaining its shape.

Preferred embodiments of the invention have been described in considerable detail, many modifications and variations to the preferred embodiments described will be apparent to a person of ordinary skill in the art. For example the powder metal parts may have various retention shapes or size or the part may have additional levels of complexity. Therefore, the invention should not be limited to the embodiments described. 

We claim:
 1. A sintered powder metal insert for being overmolded by an overmolding material, comprising a body of sintered powder metal, the body having opposed end surfaces and an outer surface extending between the end surfaces, the outer surface having one set of retention features formed in it as spaced apart recesses extending from one end surface toward the other end surface and terminating short of the other end surface and having a second set of retention features formed in the outer surface as spaced apart recesses extending from the other end surface toward the one end surface and terminating short of reaching the one end surface, the first set being angularly offset from the second set so that the features of the first set are angularly between the features of the second set.
 2. A sintered powder metal insert as claimed in claim 1, wherein the features of each set extend axially a length so as to terminate short of axially overlapping the features of the other set.
 3. A sintered powder metal insert as claimed in claim 1, wherein the features extend longitudinally further than circumferentially.
 4. A sintered powder metal insert as claimed in claim 1, wherein each feature has a radially inward surface that is generally in the shape of a section of a cylinder.
 5. A sintered powder metal insert as claimed in claim 1, wherein each feature forms an end wall where it terminates at a blind end.
 6. A sintered powder metal insert as claimed in claim 1, wherein the outer surface is generally cylindrical.
 7. A sintered powder metal insert as claimed in claim 7, wherein the end wall is in a plane that is perpendicular to the axial direction.
 8. A sintered powder metal insert as claimed in claim 1, wherein the features of the first set do not intersect each other.
 9. A sintered powder metal insert as claimed in claim 1, wherein the features of the second set do not intersect each other.
 10. A sintered powder metal insert as claimed in claim 1, wherein the insert has a bore.
 11. A sintered powder metal insert as claimed in claim 11, wherein the bore has a non-round shape so as to be driven by a shaft.
 12. A sintered powder metal insert as claimed in claim 1, wherein the features of the first set do not intersect the features of the second set.
 13. A method of making a sintered powder metal insert as claimed in claim 1, including the step of compacting powder metal in a compaction tool set including upper tooling comprising an upper die and lower tooling comprising a lower die, wherein the one set of features is formed by one of the dies and the other set of features is formed by the other die.
 14. A method as claimed in claim 13, wherein the method includes the steps of filling a first cavity of the lower die with powder metal, bringing the upper die into abutment with the lower die and thereafter moving the powder metal in the first cavity so that it occupies cavities in both dies and thereafter compressing the powder metal in said cavities.
 15. A method as claimed in claim 14, wherein the compaction tool set includes at least one core pin that together with the lower die helps define the first cavity into which powder metal is filled, said at least one core pin defining a bore in the powder metal part upon completion of compaction of the part.
 16. A method as claimed in claim 15, wherein the core pin is stepped in shape so as to define a stepped bore of a larger diameter and a smaller diameter in the powder metal part upon completion of compaction of the part.
 17. A method as claimed in claim 16, wherein a tubular punch surrounds a portion of the core pin below the first cavity and has an end face that defines an end surface of the powder metal part upon completion of compaction of the part. 